[Rails5] Fix `params` for DeleteUserWorker

This commit fixes the error:

```
  1) Admin::UsersController DELETE #user with projects deletes the user and their contributions when hard delete is specified
     Failure/Error: Users::DestroyService.new(current_user).execute(delete_user, options.symbolize_keys)

     NoMethodError:
       undefined method `symbolize_keys' for "{\"hard_delete\"=>\"true\"}":String
     # ./app/workers/delete_user_worker.rb:8:in `perform'
     # ./lib/gitlab/sidekiq_status/server_middleware.rb:5:in `call'
     # ./config/initializers/forbid_sidekiq_in_transactions.rb:35:in `block (2 levels) in <module:NoEnqueueingFromTransactions>'
     # ./app/models/user.rb:913:in `delete_async'
     # ./app/controllers/admin/users_controller.rb:148:in `destroy'
     # ./lib/gitlab/i18n.rb:50:in `with_locale'
     # ./lib/gitlab/i18n.rb:56:in `with_user_locale'
     # ./app/controllers/application_controller.rb:327:in `set_locale'
     # ./spec/controllers/admin/users_controller_spec.rb:28:in `block (3 levels) in <top (required)>'

Finished in 6.81 seconds (files took 13.9 seconds to load)
1 example, 1 failure
```

1 files changed, 1 insertions, 1 deletions

diff --git a/app/models/user.rb b/app/models/user.rb
index b0668148972..4a602ffbb05 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -910,7 +910,7 @@ class User < ActiveRecord::Base
 
   def delete_async(deleted_by:, params: {})
     block if params[:hard_delete]
-    DeleteUserWorker.perform_async(deleted_by.id, id, params)
+    DeleteUserWorker.perform_async(deleted_by.id, id, params.to_h)
   end
 
   def notification_service